U.S. patent application number 16/667294 was filed with the patent office on 2020-10-01 for scale-up of microfluidic devices.
The applicant listed for this patent is President and Fellows of Havard College. Invention is credited to Adam R. Abate, Mark Romanowsky, David A. Weitz.
Application Number | 20200306706 16/667294 |
Document ID | / |
Family ID | 1000004887273 |
Filed Date | 2020-10-01 |
United States Patent
Application |
20200306706 |
Kind Code |
A1 |
Weitz; David A. ; et
al. |
October 1, 2020 |
SCALE-UP OF MICROFLUIDIC DEVICES
Abstract
Parallel uses of microfluidic methods and devices for focusing
and/or forming discontinuous sections of similar or dissimilar size
in a fluid are described. In some aspects, the present invention
relates generally to flow-focusing-type technology, and also to
microfluidics, and more particularly parallel use of microfluidic
systems arranged to control a dispersed phase within a dispersant,
and the size, and size distribution, of a dispersed phase in a
multi-phase fluid system, and systems for delivery of fluid
components to multiple such devices.
Inventors: |
Weitz; David A.; (Bolton,
MA) ; Romanowsky; Mark; (Cambridge, MA) ;
Abate; Adam R.; (Daly City, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
President and Fellows of Havard College |
Cambridge |
MA |
US |
|
|
Family ID: |
1000004887273 |
Appl. No.: |
16/667294 |
Filed: |
October 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15288135 |
Oct 7, 2016 |
10518230 |
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16667294 |
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14710223 |
May 12, 2015 |
9486757 |
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15288135 |
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13255342 |
Jan 26, 2012 |
9056299 |
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PCT/US2010/000753 |
Mar 12, 2010 |
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14710223 |
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61223627 |
Jul 7, 2009 |
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61160184 |
Mar 13, 2009 |
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Current U.S.
Class: |
1/1 ; 422/502;
422/82 |
Current CPC
Class: |
B01L 2300/0816 20130101;
B01J 2219/00891 20130101; B01L 2300/0861 20130101; Y10T 137/0318
20150401; B01J 19/0093 20130101; B01J 2219/00975 20130101; B01J
2219/00015 20130101; B01L 2200/0673 20130101; B01L 2200/0636
20130101; B01J 2219/00833 20130101; B01F 13/0062 20130101; Y10T
137/8593 20150401; B01F 2215/0037 20130101; B01J 2219/0097
20130101; B01F 3/0811 20130101; B01J 2219/00837 20130101; B01J
2219/00831 20130101; B01L 3/502784 20130101; B01F 3/0807 20130101;
B01J 2219/00828 20130101; B01J 2219/00889 20130101; B01J 2219/00783
20130101 |
International
Class: |
B01F 13/00 20060101
B01F013/00; B01F 3/08 20060101 B01F003/08; B01L 3/00 20060101
B01L003/00; B01J 19/00 20060101 B01J019/00 |
Goverment Interests
FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with government support under Grant
No. DMR-0213805 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1-78. (canceled)
79. A system for forming droplets in microfluidic channels,
comprising: a first plane comprising: a plurality of microfluidic
interconnected regions configured for droplet formation, wherein a
microfluidic interconnected region of said plurality of
microfluidic interconnected regions is fluidically connected to a
subject fluid source, a dispersing fluid source, and a first
droplet outlet channel; and a second plane configured for fluid
distribution, comprising a common droplet outlet channel
fluidically connected to said first droplet outlet channel, wherein
said second plane is different from said first plane.
80. The system of claim 79, wherein said second plane is
substantially perpendicular to said first plane.
81. The system of claim 79, further comprising a third plane
comprising an additional plurality of microfluidic interconnected
regions configured for additional droplet formation, wherein said
additional plurality of microfluidic interconnected regions is
fluidically connected to said subject fluid source, said dispersing
fluid source, and a second droplet outlet channel, wherein said
second droplet outlet channel is fluidically connected to said
common droplet outlet channel, wherein said third plane is
different from said first plane and said second plane.
82. The system of claim 81, wherein said first plane and said third
plane are substantially parallel.
83. The system of claim 81, wherein a subject fluid distribution
channel is fluidically connected to said subject fluid source,
wherein said subject fluid source is in said second plane.
84. The system of claim 83, wherein said subject fluid distribution
channel is in a fourth plane that is different from said first
plane, said second plane and said third plane.
85. The system of claim 84, wherein said fourth plane is
substantially parallel to said first plane.
86. The system of claim 83, wherein said subject fluid distribution
channel is fluidically connected to at least two subject fluid
channels.
87. The system of claim 86, wherein said at least two subject fluid
channels are in said first plane.
88. The system of claim 87, wherein said at least two subject fluid
channels are fluidically connected to at least two microfluidic
interconnected regions of said plurality of microfluidic
interconnected regions in said first plane.
89. The system of claim 88, wherein said plurality of microfluidic
interconnected regions in said first plane are positioned in a
first array of interconnected regions and a second array of
interconnected regions, wherein said first array of interconnected
regions is fluidically connected to said first droplet outlet
channel via a first array droplet outlet channel and said second
array of interconnected regions is fluidically connected to said
first droplet outlet channel via a second array droplet outlet
channel.
90. The system of claim 83, further comprising a second subject
fluid distribution channel in said third plane that is fluidically
connected to said subject fluid source, wherein said subject fluid
distribution channel and said second subject fluid distribution
channel are fluidically connected to a common subject fluid
distribution channel in said second plane.
91. The system of claim 81, said dispersing fluid source is
fluidically connected to a dispersing fluid distribution channel
that is fluidically connected to at least one interconnected region
of said plurality of interconnected regions in said first
plane.
92. The system of claim 91, wherein said dispersing fluid
distribution channel is in a fourth plane that is different from
said first plane, said second plane and said third plane.
93. The system of claim 92, wherein said fourth plane is
substantially parallel to said first plane.
94. The system of claim 79, wherein said at least two dispersing
fluid channels are fluidically connected to at least two
microfluidic interconnected regions of said plurality of
microfluidic interconnected regions in said first plane.
95. The system of claim 87, wherein said dispersing fluid source
comprises a common dispersing fluid distribution channel.
96. The system of claim 95, further comprising a second dispersing
fluid distribution channel in said third plane, wherein said
dispersing fluid distribution channel and said second dispersing
fluid distribution channel are fluidically connected to said common
dispersing fluid distribution channel in said second plane.
97. The system of claim 79, wherein said first droplet outlet
channel is fluidically connected to at least two outlet
channels.
98. The system of claim 97, wherein said at least two outlet
channels are in said first plane.
99. The system of claim 79, wherein an aspect ratio of said droplet
outlet channel is at least 2:1.
100. The system of claim 79, wherein said microfluidic
interconnected region further comprises a dimensionally-restricted
section formed by extensions extending from an outer wall of said
microfluidic interconnected region into said microfluidic
interconnected region, wherein said dimensionally-restricted
section is positioned adjacent to an outlet of a subject fluid
channel, wherein said subject fluid channel is fluidically
connected to said subject fluid source.
101. The system of claim 100, wherein said microfluidic
interconnected region is configured to receive a dispersing fluid
from said dispersing fluid source and a subject fluid from said
subject fluid source, wherein said dimensionally-restricted section
has a shape which causes said dispersing fluid to surround and
constrict a cross-sectional shape of said subject fluid when said
subject fluid exits an outlet of said subject fluid channel.
102. The system of claim 101, wherein said dimensionally-restricted
section is fixed in size.
103. The system of claim 101, wherein said dimensionally-restricted
section comprises an annular orifice.
104. The system of claim 101, wherein said microfluidic
interconnected region is configured such that when said subject
fluid exits said outlet of said subject fluid channel, said subject
fluid is surrounded by the dispersing fluid at approximately 50% of
its circumference.
105. The system of claim 79, wherein said common droplet outlet
channel is fluidically connected to a droplet collector.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 13/255,342,
with a .sctn. 371 date of Jan. 26, 2012, which is a national stage
filing under 35 U.S.C. .sctn. 371 of International Patent
Application Serial No. PCT/US2010/000753, filed Mar. 12, 2010,
which claims the benefit of U.S. Provisional Patent Application
Ser. No. 61/160,184, filed Mar. 13, 2009, entitled "Scale-up of
Microfluidic Devices," by Romanowsky, et al., and of U.S.
Provisional Patent Application Ser. No. 61/223,627, filed Jul. 7,
2009, entitled "Scale-up of Microfluidic Devices," by Romanowsky,
et al., all of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates generally to
flow-focusing-type technology, and also to microfluidics, and more
particularly parallel use of microfluidic systems arranged to
control a dispersed phase within a dispersant, and the size, and
size distribution, of a dispersed phase in a multi-phase fluid
system, and systems for delivery of fluid components to multiple
such devices.
BACKGROUND OF THE INVENTION
[0004] The manipulation of fluids to form fluid streams of desired
configuration, discontinuous fluid streams, particles, dispersions,
etc., for purposes of fluid delivery, product manufacture,
analysis, and the like, is a relatively well-studied art. For
example, highly monodisperse gas bubbles, less than 100 microns in
diameter, have been produced using a technique referred to as
capillary flow focusing. In this technique, gas is forced out of a
capillary tube into a bath of liquid, the tube is positioned above
a small orifice, and the contraction flow of the external liquid
through this orifice focuses the gas into a thin jet which
subsequently breaks into equal-sized bubbles via a capillary
instability. In a related technique, a similar arrangement was used
to produce liquid droplets in air.
[0005] Microfluidics is an area of technology involving the control
of fluid flow at a very small scale. Microfluidic devices typically
include very small channels, within which fluid flows, which can be
branched or otherwise arranged to allow fluids to be combined with
each other, to divert fluids to different locations, to cause
laminar flow between fluids, to dilute fluids, and the like.
Significant effort has been directed toward "lab-on-a-chip"
microfluidic technology, in which researchers seek to carry out
known chemical or biological reactions on a very small scale on a
"chip," or microfluidic device. Additionally, new techniques, not
necessarily known on the macro scale, are being developed using
microfluidics. Examples of techniques being investigated or
developed at the microfluidic scale include high-throughput
screening, drug delivery, chemical kinetics measurements,
combinatorial chemistry (where rapid testing of chemical reactions,
chemical affinity, and micro structure formation are desired), as
well as the study of fundamental questions in the fields of
physics, chemistry, and engineering.
[0006] The field of dispersions is well-studied. A dispersion (or
emulsion) is a mixture of two materials, typically fluids, defined
by a mixture of at least two incompatible (immiscible) materials,
one dispersed within the other. That is, one material is broken up
into small, isolated regions, or droplets, surrounded by another
phase (dispersant, or constant phase), within which the first phase
is carried. Examples of dispersions can be found in many industries
including the food and cosmetic industry. For example, lotions tend
to be oils dispersed within a water-based dispersant. In
dispersions, control of the size of droplets of dispersed phase can
effect overall product properties, for example, the "feel" of a
lotion.
[0007] Formation of dispersions typically is carried out in
equipment including moving parts (e.g., a blender or device
similarly designed to break up material), which can be prone to
failure and, in many cases, is not suitable for control of very
small dispersed phase droplets. Specifically, traditional
industrial processes typically involve manufacturing equipment
built to operate on size scales generally unsuitable for precise,
small dispersion control. Membrane emulsification is one small
scale technique using micron-sized pores to form emulsions.
However, polydispersity of the dispersed phase can in some cases be
limited by the pore sizes of the membrane.
[0008] Batch production of discontinuous fluids are prone to
difficulties in product uniformity. These problems can be
compounded for complex structures such as double emulsions
(drops-in-drops) or triple emulsions (drops-in-drops-in-drops). A
further difficulty for double or triple emulsions is poor
encapsulation efficiency, where substantial amounts of the
innermost phase leak out into the outermost phases, which can limit
the usefulness of such emulsions as carriers for valuable or
volatile compounds such as drugs, flavors, or fragrances.
Microfluidic devices, by contrast, can produce multiple emulsions
with extremely high uniformity and encapsulation efficiency,
essentially by regulating emulsion formation on the
individual-droplet level. Such control comes at the cost of forming
emulsion droplets essentially one at a time, each microfluidic
device producing only small amounts of product on the order of
fractions of a milliliter per hour. The present invention in part
involves appreciation of the need for scale-up of the products of
microfluidic devices.
[0009] While many techniques involving control of multi-phase
systems exists, there is a need for improvement in control of size
of dispersed phase, size range (polydispersity), and other
factors.
SUMMARY OF THE INVENTION
[0010] The present invention relates generally to
flow-focusing-type technology, and also to microfluidics, and more
particularly parallel use of microfluidic systems arranged to
control a dispersed phase within a dispersant, and the size, and
size distribution, of a dispersed phase in a multi-phase fluid
system, and systems for delivery of fluid components to multiple
such devices. The subject matter of the present invention involves,
in some cases, interrelated products, alternative solutions to a
particular problem, and/or a plurality of different uses of one or
more systems and/or articles.
[0011] In one aspect, a method is provided. The methods comprises
introducing a subject fluid into an inlet of a channel and
expelling separate portions of the subject fluid from a plurality
of microfluidic outlets each fluidly connected to the inlet,
simultaneously, while surrounding at least one of the separate
portions of the subject fluid at least in part with a dispersing
fluid.
[0012] In another aspect, a system for forming droplets in
microfluidic channels in parallel is provided. The system comprises
a distribution channel having an inlet fluidly connected to a
plurality of microfluidic subject fluid outlets, each outlet
defining a portion of a microfluidic interconnected region in fluid
communication with at least one dispersing fluid channel fluidly
connectable to a source of a dispersing fluid.
[0013] In another aspect, a system for forming droplets in
microfluidic channels in parallel is provided. The system comprises
an interconnected region joining a subject fluid channel for
carrying a subject fluid, and a dispersing fluid channel for
carrying a dispersing fluid, wherein at least a portion defining an
outer wall of the interconnected region and a portion defining an
outer wall of the subject fluid channel are portions of a single
integral unit.
[0014] The subject matter of this application may involve, in some
cases, interrelated products, alternative solutions to a particular
problem, and/or a plurality of different uses of a single system or
article.
[0015] Other advantages, features, and uses of the invention will
become apparent from the following detailed description of
non-limiting embodiments of the invention when considered in
conjunction with the accompanying drawings, which are schematic and
which are not intended to be drawn to scale. In the figures, each
identical or nearly identical component that is illustrated in
various figures typically is represented by a single numeral. For
purposes of clarity, not every component is labeled in every
figure, nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. In cases
where the present specification and a document incorporated by
reference include conflicting disclosure, the present specification
shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Non-limiting embodiments of the present invention will be
described by way of example with reference to the accompanying
figures, which are schematic and are not intended to be drawn to
scale. In the figures, each identical or nearly identical component
illustrated is typically represented by a single numeral. For
purposes of clarity, not every component is labeled in every
figure, nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. In the
figures:
[0017] FIG. 1 is a schematic illustration of a fluid distribution
article according to an embodiment.
[0018] FIG. 2 is a schematic illustration of a three-dimensional
parallel microfluidic device according to an embodiment.
[0019] FIG. 3 is a schematic illustration of a one-dimensional
parallel microfluidic device according to an embodiment.
[0020] FIG. 4 is a schematic illustration of a two-dimensional
parallel microfluidic device according to an embodiment.
[0021] FIG. 5 is a schematic illustration of a microfluidic device
of the invention according to an embodiment.
[0022] FIG. 6 is a schematic cross-sectional view through line 44
of FIG. 5.
[0023] FIG. 7 is a photograph of a two-dimensional parallel
microfluidic device according to an embodiment.
[0024] FIG. 8 is a schematic illustration of a parallel
microfluidic device according to an embodiment.
[0025] FIG. 9 is a schematic illustration of a parallel
microfluidic device according to an embodiment.
[0026] FIG. 10 is a schematic illustration of a parallel
microfluidic device according to an embodiment.
[0027] FIG. 11 is a schematic illustration of a parallel
microfluidic device according to an embodiment.
[0028] FIG. 12 is a photograph of a microfluidic device according
to an embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The following documents are incorporated herein by reference
in their entirety: U.S. Pat. No. 5,512,131, issued Apr. 30, 1996 to
Kumar, et al.; International Patent Publication WO 96/29629,
published Jun. 26, 1996 by Whitesides, et al.; U.S. Pat. No.
6,355,198, issued Mar. 12, 2002 to Kim, et al.; International
Patent Publication WO 01/89787, published Nov. 29, 2001 by
Anderson, et al.; International Patent Publication WO2004/091763,
published Oct. 28, 2004 by Link et al.; International Patent
Publication WO2004/002627, published Jan. 8, 2004 by Stone et al.;
International Patent Publication WO2005/021151, published Mar. 10,
2005; WO2007/089541, published Aug. 9, 2007 by Ahn et al.;
WO2008/121342, published Oct. 9, 2008 by Chu et al.; WO2006/096571
published Sep. 14, 2006 by Weitz et al. Also incorporated herein by
reference are U.S. Provisional Patent Application Ser. No.
61/160,020, filed on Mar. 13, 2009, entitled "Controlled Creation
of Emulsions, Including Multiple Emulsions," by Weitz, et al.; U.S.
Provisional Patent Application Ser. No. 61/160,184, filed Mar. 13,
2009, entitled "Scale-up of Microfluidic Devices," by Romanowsky,
et al.; and U.S. Provisional Patent Application Ser. No.
61/223,627, filed Jul. 7, 2009, entitled "Scale-up of Microfluidic
Devices," by Romanowsky, et al.
[0030] Systems and techniques for parallel use of microfluidic
methods and devices for focusing and/or forming discontinuous
sections of similar or dissimilar size in a fluid are provided. In
one aspect, a fluid distribution article is used to distribute
fluid from one input to a plurality of outputs. Using the disclosed
methods and articles, a plurality of microfluidic devices may be
connected in three dimensions. Microfluidic systems and the
techniques are described in which, in some cases, it can be
important to control back pressure and flow rate such that a
microfluidic process, such as droplet formation, can be carried out
reproducibly and consistently across a variety of similar or
identical process locations. This is challenging in a microfluidic
environment and it is not seen where the prior art provides any
ability to achieve this. The present invention does so. In some
cases, channel dimensions are chosen that allow pressure variations
within parallel devices to be substantially reduced.
[0031] In some embodiments, the present invention involves devices
and techniques associated with manipulation of multiphase materials
in parallel. While those of ordinary skill will recognize that any
of a wide variety of materials including various numbers of phases
can be manipulated in accordance with certain embodiments of the
invention, various embodiments of the invention finds use,
generally, with two-phase systems of incompatible fluids. A
"fluid," as used herein, means any substance which can be urged to
flow through devices described below to achieve the benefits
discussed herein. Those of ordinary skill in the art will recognize
which fluids have viscosity appropriate for use in accordance with
various embodiments of the invention, i.e., which substances are
"fluids." It should be appreciated that a substance may be a fluid,
for purposes of certain embodiments of the invention, under one set
of conditions but may, under other conditions, have viscosity too
high for use as a fluid. Where the material or materials behave as
fluids under at least one set of conditions compatible with certain
embodiments of the invention, they are included as potential
materials for manipulation.
[0032] In one set of embodiments, the present invention involves
formation of drops of a dispersed phase within a dispersant, of
controlled size and size distribution, in a flow system (preferably
a microfluidic system) free of moving parts to create drop
formation. That is, at the location or locations at which drops of
desired size are formed, the device is free of components that move
relative to the device as a whole to affect drop formation or size.
For example, where drops of controlled size are formed, they are
formed without parts that move relative to other parts of the
device that define a channel within the drops flow. This can be
referred to as "passive control" of drop size, or "passive breakup"
where a first set of drops are broken up into smaller drops.
[0033] Parallel microfluidic devices can be used to produce
large-scale quantities of product by integrating many individual
devices onto the same monolithic chip. In some cases, a parallel
microfluidic device can generate emulsions in quantities of liters
per day per integrated chip, or even greater. For example, at least
about 200 mL per day per integrated chip, at least about 1 L per
day per integrated chip, at least about 2 L per day per integrated
chip, at least about 5 L per day per integrated chip, at least
about 50 L per day per integrated chip, at least about 500 L per
day per integrated chip, or even more could be produced.
[0034] In some embodiments, parallel scale-up is accompanied by a
fluid distribution article for inputting fluids to, and collecting
product from, an array of devices. As described in more detail
below, the fluid distribution article and array of devices can be
fabricated using known methods. The fluid distribution article can
be used to operate an arbitrary number of microfluidic devices with
a minimum number of interfaces to external fluid supplies and
collectors, connect a high density array of devices, and promote a
long functioning lifetime of the integrated device through system
redundancy. Referring now to FIG. 1, a one-dimensional parallel
microfluidic system 300 according to one embodiment of the present
invention is illustrated schematically. A fluid distribution
article 190 is used to distribute fluid from inputs 130 and 140 to
a parallel drop formation array 200, and the resulting emulsion
formed by the drop formation array exits through output 150. The
fluid distribution article allows fluid entering, for example, a
single channel 135 to flow into channel 160 and be distributed to a
plurality of channels 165, which enter the drop formation devices
in system 200.
[0035] FIG. 2, one embodiment of the present invention, illustrates
schematically the assembly of three-dimensional parallel
microfluidic system 100 of drop formation devices 120. System 100
includes two dimensional arrays 200 of drop formation devices 120.
As described in FIG. 1, in this embodiment of the invention a first
fluid (i.e., a dispersant fluid such as oil) is flowed through
input 130 into channel 135, a second fluid is flowed through input
140 into channel 145, and an emulsion produced by the interaction
of the first fluid and the second fluid in drop formation devices
120 flow out of the system through channel 155 and output 150.
Distribution plate 190, which includes channels 160, 170, and 180,
is in a different plane than the plane of the two-dimensional drop
formation array 200, such that channels 160, 170, and 180 are in a
different plane than cross-channels 210, 220, and 230. Channels
165, 175, and 185, connect channels 160, 170, and 180,
respectively, to channels 210, 220, and 230, respectively.
[0036] In some embodiments, the fluid distribution article includes
one or more layers of fluidic channels stacked above the layer(s)
of microfluidic devices (FIG. 1). Although "top," "bottom,"
"above," "below," etc. are used to define certain portions and
perspectives of systems of various embodiments of the invention, it
is to be understood that the systems can be used in orientations
different from those described. The fluid distribution article can
serve one-dimensional (1-D), two-dimensional (2-D), and/or
three-dimensional (3-D) arrays of devices in a scalable, parallel
configuration. For example, a 1-D linear array of devices may be
served by a single set of fluidic channels as shown in FIG. 3,
which illustrates 1-D array 400 of microfluidic devices 120 in
fluid communication with channels 210, 220, and 230. In this
embodiment, channels 210, 220, and 230 are placed directly over the
corresponding inlet or outlet of every device in the array, i.e.,
channel 210 supplying a first fluid to every device through inlets
211, channel 220 supplying a second fluid to every device through
inlets 221, and channel 230 collecting the product from each device
from outlets 231. In some embodiments, the fluid distribution
article channels have at least one aperture each (e.g., apertures
212, 222, and 232) on the top side of the channel for supplying
fluid to the corresponding channels and/or collecting product from
the corresponding channels.
[0037] A similar design can be used to create a 2-D array of
devices with each 1-D sub-array served by its own set of
distribution channels as shown in FIG. 4, which depicts a 2-D array
500 of microfluidic devices 120, a first set of distribution
channels 210, 220, and 230 in fluid communication with each 1-D
array of devices, and a second set of distribution channels 160,
170, and 180 in fluid communication with the first set of
distribution channels 210, 220, and 230, respectively. Channels
160, 170, and 180 may have at least two sets of apertures, a first
set of apertures 165, 175, and 185 that connect channels 160, 170,
and 180 to channels 210, 220, and 230, respectively, and a second
set of apertures 166, 167, and 168 through which fluid can flow
into array 500 and/or product can be collected from array 500.
[0038] In some embodiments, the distribution channels in each set
of distribution channels are incorporated into a single layer.
Thus, 2-D array 500 can be constructed by fabricating devices 120
in a first layer, distribution channels 210, 220, and 230 in a
second layer on top of the first layer, and distribution channels
160, 170, and 180 in a third layer on top of the second layer.
Those skilled in the art will recognize that the order of assembly
may be different.
[0039] In some cases, a 3-D array is constructed by connecting
units of 2-D arrays, as shown in FIG. 2. In some embodiments, a set
of distribution channels (e.g., channels 135, 145, and 155 in FIG.
2) are used to fluidically connect units of 2-D arrays. A 3-D array
may be constructed in a variety of conformations, for example by
stacking 2-D arrays, placing 2-D arrays side-by-side, etc. As shown
in FIG. 2, array 100 may be operated with a single set of inputs
and/or outputs 130, 140, and 150.
[0040] In some embodiments, distribution channels and devices may
be incorporated in a single layer. A non-limiting example is shown
in FIG. 8, which illustrates an array 600 with two distribution
channels 610 and 612 that serve two devices 620. In this example,
distribution channel 610 contains a continuous phase (e.g., an oil)
fed by an inlet 614, and distribution channel 612 contains a
dispersed phase (e.g., an aqueous solution) fed by an inlet 616.
The distribution channels feed into droplet-making devices 620, and
the droplets 622 exit the devices through outlets 624. It should be
understood that more than two devices may be operated using the
layout depicted in FIG. 8, for example, by replicating additional
devices 620 side-by-side and extending distribution channels 610
and 612 along their respective longitudinal axes. It should also be
understood that arrangements other than linear arrangements may be
used. For example, one or more of the devices and/or distribution
channels may be curved or bent. For instance, distribution channels
610 and 612 and devices 620 may be arranged as shown in FIG. 9,
which illustrates two-dimensional array 650.
[0041] In another non-limiting example, devices and distribution
channels constructed for producing droplet-in-droplet emulsions may
be fabricated in a single layer. FIG. 10 depicts one embodiment of
this example and shows an array 700 with two distribution channels
710 and 712 serving two devices 720. In this example, distribution
channel 710 contains a continuous phase fed by inlet 714, and
distribution channel 712 contains a dispersed phase fed by inlet
716. Droplets 722 of the continuous phase are generated by flowing
the continuous phase into a channel 730 containing the dispersed
phase. Droplets 724, each containing a continuous phase droplet
722, are generated by flowing droplets 722 into channels 732.
Droplets 724 exit the devices through outlets 726. FIG. 12 shows
another embodiment of a device constructed for producing
droplet-in-droplet emulsions.
[0042] Such droplets may be useful, for example, for producing
particles such as core/shell-type particles. It should be
understood that higher order emulsions (i.e., triple emulsions,
quadruple emulsions, etc.) may also be generated using designs such
as this one. For example, by flowing droplets 724 into a channel
containing another phase instead of into outlet 726, a triple
emulsion may be generated. For instance, an oil-water-oil emulsion
may be created by flowing an oil phase into an aqueous phase to
generate oil droplets suspended in the aqueous phase, flowing the
oil droplets suspended in the aqueous phase into an oil phase to
generate an oil-in-water emulsion suspended in the oil phase (i.e.,
droplets containing an oil droplet suspended in an aqueous
droplet), and flowing the oil-in-water emulsion suspended in the
oil phase into an aqueous phase to generate an oil-water-oil
emulsion (i.e., droplets containing an oil droplet suspended in an
aqueous droplet suspended in an oil droplet).
[0043] In some embodiments, one or more of the phases, such as the
aqueous phase, may contain a surfactant. For example, the aqueous
phase may contain sodium dodecyl sulfate. As discussed herein, the
oil phase may be any suitable material. Non-limiting examples of
suitable oil phases include 1-octanol and HFE-7500 oil with 1.8%
(by weight) "R22" surfactant as the continuous phase [R22 is the
ammonium salt of Krytox.RTM. 157 FSL oil, a commercially available
perfluorinated polyether (Dupont)].
[0044] In still another non-limiting example, array 650 shown in
FIG. 9 may be operated differently by changing the direction of
flow and the type of fluid flowing through the channels, as shown
in FIG. 11. FIG. 11 illustrates array 800 with devices 820
generating four different dispersed phases surrounded by a
continuous phase. (The four dispersed phases may have the same or
different compositions, depending on the application.) In this
example, distribution channel 610 contains a continuous phase fed
by inlet 614, and collection channel 810, containing the continuous
phase fed by channels 840, collects droplets 822, 824, 826, and
828, which exit channel 810 through outlet 816. Inlets 830, 832,
834, and 836 each flow a different dispersed phase into collection
channel 810 through channels 840 to generate droplets 822, 824,
826, and 828, respectively. This may be used, for example, to
generate libraries of different droplets in parallel. It should be
understood that inlets 830, 832, 834, and 836 may flow any
combination of the same or different fluids. It should be
understood that the arrays shown in FIGS. 8-11 may also be
parallelized in three dimensions in other embodiments.
[0045] An array, such as depicted in FIG. 11, may lead in certain
cases to substantial time savings for library generation as
compared to traditional methods which involve producing droplets
serially in a first step and then mixing the droplets together in a
separate second step. This may be advantageous, for example, when
the library contains one or more sensitive compositions prone to
degradation. In some cases, using a common pressure differential to
drive formation of each type of droplet may improve uniformity in
the size of the droplets. In certain embodiments, using a separate
inlet channel for each dispersed phase can decrease the potential
for contamination of the droplets as compared to instances, for
example, when the same inlet channel is reused to flow different
dispersed phases.
[0046] The fluid distribution article channels may be fabricated
with dimensions (height, width, and/or length) much larger than the
dimensions of the device microchannels, which can allow the
pressure drop along the fluid distribution article channels to be
essentially negligible compared to the pressure drop across each
microfluidic device. As described in more detail below, such a
design can prevent hydrodynamic coupling of the devices, ensure
their independent and stable performance, and/or partition fluid
equally between the devices. Thus, a single set of distribution
channels can serve a linear array of microfluidic devices and
reduce their interface to a single set of inlet/outlet apertures
without substantially affecting the performance of the devices.
[0047] A fluid distribution article can be used to interface with
an array of many independent microfluidic devices, thereby allowing
an assembly comprising an arbitrary number of devices to be served
with a single set of inlets and outlets. In some embodiments, the
methods and articles of the present invention allow scaling to at
least about 100 devices, at least about 1,000 devices, at least
about 10,000 devices, at least about 100,000 devices, or even
more.
[0048] In some cases, the devices are arranged in a high density
array. For example, the spacing between devices may be less than
100 microns, less than 50 microns, less than 20 microns, less than
10 microns etc. The use of a fluid distribution article also allows
denser packing of parallel devices than can be achieved using
single-layer schemes since channel crossing must be avoided in
single-layer schemes.
[0049] The total flow rate of fluid entering and/or exiting the
assembly may be at least about 100 mL per hour, at least about 1 L
per hour, at least about 10 L per hour, at least about 100 L per
hour, at least about 1000 L per hour, or even more.
[0050] In one embodiment, an article of the invention is may be
constructed containing a plurality of devices arranged in three
dimensions (e.g. a cube-like structure). For example, such an
article may contain at least 50, 100, 200, 400, 600, or even 10,000
devices. In certain instances, an article containing at least such
numbers of devices may occupy a volume of less than 5 cm.sup.3. The
present invention discloses that a single microfluidic device may
have a pressure P and that connecting a plurality of such devices
also each having a pressure P using the disclosed fluid
distribution articles does not cause a substantial increase in the
pressure, e.g., the pressure of an article having 10,000 devices,
each with pressure P may be far less than 10,000.times.P. In some
instances, the pressure may be less than 10.times.P, less than
5.times.P, less than 2.times.P, etc. In certain embodiments, the
pressure of a system having a plurality of devices has a pressure
essentially equal to P. In this aspect of the invention, in various
embodiments, an article containing a number of devices as described
above, where each device has a pressure P, with a plurality of
devices connected as described herein, each device having a
pressure P no more than 5% different than any other pressure P,
does not cause an increase in overall pressure of the overall
device more than 25%, 20%, 15%, 10%, 5%, or even 2% more than P
itself.
[0051] A further advantage of the present invention is that each
device within an array operates essentially independently from the
other devices in the array. Thus, if a device clogs or otherwise
degrades, the other devices in the array can continue to
operate.
[0052] An array of devices connected as described herein using a
fluid distribution article also undergoes a very short turn-on
transient behavior, in contrast to single-layer fan-out schemes
that suffer from long-lived oscillations before steady-state
operation is reached. For example, the turn-on transient behavior
in a device of the present invention may be less than about 10
minutes, less than about 5 minutes, less than about 1 minute, less
than about 0.1 minutes, etc.
[0053] Pressure oscillation due to hydrodynamic coupling is a
common problem in microfluidic devices, particularly when
elastomeric materials, such as PDMS, are used in the fabrication of
the devices. For example, fluid pumped into a channel in an
elastomeric microfluidic device can cause expansion and contraction
of the channel thereby introducing a pressure wave in the fluid. In
embodiments where the channel serves a plurality of microfluidic
devices, a pressure wave can introduce fluctuations in the pressure
of the fluid feeding into each of the devices connected to the
channel. In some embodiments, the present invention substantially
avoids these pressure fluctuations by controlling the volume of the
channels feeding the devices. In some cases, a pressure change in a
device may be relieved by the fluid distribution channel thereby
essentially preventing the pressure change from affecting another
device. For example, a fluid distribution channel connected to a
first and second device that are in fluid communication with each
other can allow the first and second device to be decoupled from
each other.
[0054] The following tests will be useful for allowing one skilled
in the art to design an array of microfluidic devices substantially
without hydrodynamic coupling. For a 1-D array of N essentially
identical devices connected by a distribution channel, each device
has a hydrodynamic resistance value R.sub.d, and the distribution
channel has a hydrodynamic resistance R.sub.c1 over the distance
between adjacent devices (i.e., the resistance per segment). It is
understood that the resistance may be different, but within the
same order of magnitude, between inlets and outlets of a device.
For example, the resistance between the oil inlet and the device
outlet may be different in comparison to the resistance between the
water inlet and the device outlet. If R.sub.c1 is much less than
R.sub.d, the fractional difference in flow rates between the first
and last devices in the array is less than N*R.sub.c1/R.sub.d. In
some cases, this quantity is maintained below 50%, below 40%, below
30%, below 20%, below 10%, below 1%, below 0.5%, below 0.1%,
etc.
[0055] For a 2-D array of M.times.N devices, arranged in an
M.times.N grid with M rows of devices, each containing N devices
and each row being served by its own set of first-generation linear
distribution channels, the hydrodynamic resistance between the
inlet of a first-generation distribution channel and the
corresponding outlet is approximately R.sub.d/N, assuming that
R.sub.c1 is much less than R.sub.d. To deliver fluid equally to
each of the M rows of devices, the second generation distribution
channels should have resistance per segment R.sub.c2 much less than
R.sub.d/N. In this case, the fractional difference in flow rates
between the first and last rows of devices is less than
M*N*R.sub.c2/R.sub.d. To maintain essentially equal flow per device
at the same precision as for the 1-D array, the second-generation
channels should be designed to have R.sub.c2<R.sub.c1/M.
[0056] Similarly, in a 3-D array of K.times.M.times.N devices,
arranged in K planes of M.times.N grids, the third generation of
channels should have resistance per segment
R.sub.c3<R.sub.c2/K.
[0057] Referring now to FIG. 5, one embodiment of the present
invention, in the form of a microfluidic system 26, is illustrated
schematically in cross-section (although it will be understood that
a top view of system 26, absent top wall 38 of FIG. 6, would appear
similar). Although "top" and "bottom" are used to define certain
portions and perspectives of various systems of the invention, it
is to be understood that the systems can be used in orientations
different from those described. For reference, it is noted that the
system is designed such that fluid flows optimally from left to
right per the orientation of FIG. 5.
[0058] System 26 includes a series of walls defining regions of the
microfluidic system via which the system will be described. A
microfluidic interconnected region 28 is defined in the system by
walls 29, and includes an upstream portion 30 and a downstream
portion 32, connected to an outlet further downstream which is not
shown in FIG. 5. In the embodiment illustrated in FIG. 5, a subject
fluid channel 34, defined by side walls 31, is provided within the
outer boundaries of interconnected region 28. Subject fluid channel
34 has an outlet 37 between upstream portion 30 and downstream
portion 32 of interconnected region 28. The system is thus arranged
to deliver a subject fluid from channel 34 into the interconnected
region between the upstream portion and the downstream portion.
[0059] FIG. 6, a cross-sectional illustration through line 4-4 of
FIG. 5 shows (in addition to some of the components shown in FIG.
5, such as walls 29 and 31) a bottom wall 36 and a top wall 38
which, together with walls 29 and 31, defining continuous region 28
(at upstream portion 30 thereof) and subject fluid channel 34. It
can be seen that interconnected region 28, at upstream portion 30,
includes two separate sections, separated by subject fluid channel
34. The separate sections are interconnected further
downstream.
[0060] Referring again to FIG. 5, interconnected region 28 includes
a dimensionally-restricted section 40 formed by extensions 42
extending from side walls 29 into the interconnected region. Fluid
flowing from upstream portion 30 to downstream portion 32 of the
interconnected region must pass through dimensionally-restricted
section 40 in the embodiment illustrated. Outlet 37 of subject
fluid channel 34 is positioned upstream of the
dimensionally-restricted section. In the embodiment illustrated,
the downstream portion of interconnected region 28 has a central
axis 44, which is the same as the central axis of subject fluid
channel 34. That is, the subject fluid channel is positioned to
release subject fluid upstream of the dimensionally-restricted
section, and in line with the dimensionally-restricted section. As
arranged as shown in FIG. 5, subject fluid channel 34 releases
subject fluid into an interior portion of interconnected region 28.
That is, the outer boundaries of the interconnected region are
exterior of the outer boundaries of the subject fluid channel. At
the precise point at which fluid flowing downstream in the
interconnected region meets fluid released from the subject fluid
channel, the subject fluid is surrounded at least in part by the
fluid in the interconnected region, but is not completely
surrounded by fluid in the interconnected region. Instead, it is
surrounded through approximately 50% of its circumference, in the
embodiment illustrated. Portions of the circumference of the
subject fluid are constrained by bottom wall 36 and top wall
38.
[0061] In the embodiments illustrated, the dimensionally-restricted
section is an annular orifice, but it can take any of a varieties
of forms. For example, it can be elongate, ovoid, square, or the
like. Preferably, it is shaped in any way that causes the
dispersing fluid to surround and constrict the cross-sectional
shape of the subject fluid. The dimensionally-restricted section is
non-valved in preferred embodiments. That is, it is an orifice that
cannot be switched between an open state and a closed state, and
typically is of fixed size.
[0062] Although not shown in FIGS. 5 and 6, one or more
intermediate fluid channels can be provided in the arrangement of
FIGS. 5 and 6 to provide an encapsulating fluid surrounding
discontinuous portions of subject fluid produced by action of the
dispersing fluid on the subject fluid. In one embodiment, two
intermediate fluid channels are provided, one on each side of
subject fluid channel 34, each with an outlet near the outlet of
the subject fluid channel. In some cases, discontinuous sections of
the subject fluid are created by introducing intermediate fluid
between the subject fluid and the dispersing fluid, with each
section surrounded by a shell of the intermediate fluid. In some
embodiments, the shell is hardened. The following definitions will
assist in understanding certain aspects of the invention. Also
included, within the list of definitions, are sets of parameters
within which certain embodiments of the invention fall.
[0063] "Channel," as used herein, means a feature on or in an
article (substrate) that can at least partially confine and direct
the flow of a fluid, and that has an aspect ratio (length to
average cross sectional dimension) of at least 2:1, more typically
at least 3:1, 5:1, or 10:1. The feature can be a groove or other
indentation of any cross-sectional shape (curved, square or
rectangular) and can be covered or uncovered. In embodiments where
it is completely covered, at least one portion of the channel can
have a cross-section that is completely enclosed, or the entire
channel may be completely enclosed along its entire length with the
exception of its inlet and outlet. An open channel generally will
include characteristics that facilitate control over fluid
transport, e.g., structural characteristics (an elongated
indentation) and/or physical or chemical characteristics
(hydrophobicity vs. hydrophilicity) or other characteristics that
can exert a force (e.g., a containing force) on a fluid. The fluid
within the channel may partially or completely fill the channel. In
some cases where an open channel is used, the fluid may be held
within the channel, for example, using surface tension (i.e., a
concave or convex meniscus). The channel may be of any size, for
example, having a largest dimension perpendicular to fluid flow of
less than about 5 or 2 millimeters, or less than about 1
millimeter, or less than about 500 microns, less than about 200
microns, less than about 100 microns, or less than about 50 or 25
microns. In some cases the dimensions of the channel may be chosen
such that fluid is able to freely flow through the reactor. The
dimensions of the channel may also be chosen, for example, to allow
a certain volumetric or linear flowrate of fluid in the channel. Of
course, the number of channels and the shape of the channels can be
varied by any method known to those of ordinary skill in the art.
In the embodiments illustrated in the accompanying figures, all
channels are completely enclosed. "Channel", as used herein, does
not include a space created between a channel wall and an
obstruction. Instead, obstructions, as defined herein, are
understood to be contained within channels. Larger channels, tubes,
etc. can be used in microfluidic device for a variety of purposes,
e.g., to store fluids in bulk and to deliver fluids to components
of various embodiments of the invention.
[0064] In some, but not all embodiments, all components of the
systems described herein are microfluidic. "Microfluidic", as used
herein, refers to a device, apparatus or system including at least
one fluid channel having a cross-sectional dimension of less than 1
millimeter (mm), and a ratio of length to largest cross-sectional
dimension of at least 3:1, and "microfluidic channel" is a channel
meeting these criteria. Cross-sectional dimension is measured
perpendicular to the direction of fluid flow. Most fluid channels
in certain components of the invention have maximum cross-sectional
dimensions less than 2 millimeters, and preferably 1 millimeter. In
one set of embodiments, all fluid channels, at least at regions at
which one fluid is dispersed by another, are microfluidic or of
largest cross sectional dimension of no more than 2 millimeters. In
another embodiment, all fluid channels associated with fluid
dispersion, formed in part by a single component (e.g. an etched
substrate or molded unit) are microfluidic or of maximum dimension
of 2 millimeters. Of course, larger channels, tubes, etc. can be
used to store fluids in bulk and to deliver fluids to components of
other embodiments of the invention.
[0065] A "microfluidic interconnected region," as used herein,
refers to a portion of a device, apparatus or system including two
or more microfluidic channels in fluid communication.
[0066] The "cross-sectional dimension" of the channel is measured
perpendicular to the direction of fluid flow. Most fluid channels
in components of various embodiments of the invention have maximum
cross-sectional dimensions less than 2 mm, and in some cases, less
than 1 mm. In one set of embodiments, all fluid channels are
microfluidic or have a largest cross sectional dimension of no more
than 2 mm or 1 mm. In another embodiment, the fluid channels may be
formed in part by a single component (e.g. an etched substrate or
molded unit). Of course, larger channels, tubes, chambers,
reservoirs, etc. can be used to store fluids in bulk and to deliver
fluids to components of various embodiments of the invention. In
one set of embodiments, the maximum cross-sectional dimension of
all active fluid channels is less than 500 microns, less than 200
microns, less than 100 microns, less than 50 microns, or less than
25 microns. Devices and systems may include channels having
non-microfluidic portions as well.
[0067] The fluidic droplets within the channels may have a
cross-sectional dimension smaller than about 90% of an average
cross-sectional dimension of the channel, and in certain
embodiments, smaller than about 80%, about 70%, about 60%, about
50%, about 40%, about 30%, about 20%, about 10%, about 5%, about
3%, about 1%, about 0.5%, about 0.3%, about 0.1%, about 0.05%,
about 0.03%, or about 0.01% of the average cross-sectional
dimension of the channel.
[0068] As used herein, "integral" means that portions of components
are joined in such a way that they cannot be separated from each
other without cutting or breaking the components from each
other.
[0069] A "droplet," as used herein is an isolated portion of a
first fluid that is completely surrounded by a second fluid. It is
to be noted that a droplet is not necessarily spherical, but may
assume other shapes as well, for example, depending on the external
environment. In one embodiment, the droplet has a minimum
cross-sectional dimension that is substantially equal to the
largest dimension of the channel perpendicular to fluid flow in
which the droplet is located.
[0070] The "average diameter" of a population of droplets is the
arithmetic average of the diameters of the droplets. Those of
ordinary skill in the art will be able to determine the average
diameter of a population of droplets, for example, using laser
light scattering or other known techniques. The diameter of a
droplet, in a non-spherical droplet, is the mathematically-defined
average diameter of the droplet, integrated across the entire
surface. As non-limiting examples, the average diameter of a
droplet may be less than about 1 mm, less than about 500
micrometers, less than about 200 micrometers, less than about 100
micrometers, less than about 75 micrometers, less than about 50
micrometers, less than about 25 micrometers, less than about 10
micrometers, or less than about 5 micrometers. The average diameter
of the droplet may also be at least about 1 micrometer, at least
about 2 micrometers, at least about 3 micrometers, at least about 5
micrometers, at least about 10 micrometers, at least about 15
micrometers, or at least about 20 micrometers in certain cases.
[0071] As used herein, a "fluid" is given its ordinary meaning,
i.e., a liquid or a gas. The fluid may have any suitable viscosity
that permits flow. If two or more fluids are present, each fluid
may be independently selected among essentially any fluids
(liquids, gases, and the like) by those of ordinary skill in the
art, by considering the relationship between the fluids. The fluids
may each be miscible or immiscible. For example, two fluids can be
selected to be immiscible within the time frame of formation of a
stream of fluids, or within the time frame of reaction or
interaction. Where the portions remain liquid for a significant
period of time then the fluids should be significantly immiscible.
Where, after contact and/or formation, the dispersed portions are
quickly hardened by polymerization or the like, the fluids need not
be as immiscible. Those of ordinary skill in the art can select
suitable miscible or immiscible fluids, using contact angle
measurements or the like, to carry out various techniques of the
invention.
[0072] As used herein, a first entity is "surrounded" by a second
entity if a closed loop can be drawn around the first entity
through only the second entity. A first entity is "completely
surrounded" if closed loops going through only the second entity
can be drawn around the first entity regardless of direction. In
one aspect, the first entity may be a cell, for example, a cell
suspended in media is surrounded by the media. In another aspect,
the first entity is a particle. In yet another aspect of the
invention, the entities can both be fluids. For example, a
hydrophilic liquid may be suspended in a hydrophobic liquid, a
hydrophobic liquid may be suspended in a hydrophilic liquid, a gas
bubble may be suspended in a liquid, etc. Typically, a hydrophobic
liquid and a hydrophilic liquid are substantially immiscible with
respect to each other, where the hydrophilic liquid has a greater
affinity to water than does the hydrophobic liquid. Examples of
hydrophilic liquids include, but are not limited to, water and
other aqueous solutions comprising water, such as cell or
biological media, ethanol, salt solutions, etc. Examples of
hydrophobic liquids include, but are not limited to, oils such as
hydrocarbons, silicon oils, fluorocarbon oils, organic solvents
etc.
[0073] The term "determining," as used herein, generally refers to
the analysis or measurement of a species, for example,
quantitatively or qualitatively, or the detection of the presence
or absence of the species. "Determining" may also refer to the
analysis or measurement of an interaction between two or more
species, for example, quantitatively or qualitatively, or by
detecting the presence or absence of the interaction. Example
techniques include, but are not limited to, spectroscopy such as
infrared, absorption, fluorescence, UV/visible, FTIR ("Fourier
Transform Infrared Spectroscopy"), or Raman; gravimetric
techniques; ellipsometry; piezoelectric measurements; immunoassays;
electrochemical measurements; optical measurements such as optical
density measurements; circular dichroism; light scattering
measurements such as quasielectric light scattering; polarimetry;
refractometry; or turbidity measurements.
[0074] The invention, in some aspects, provides for formation of
discontinuous, or isolated, regions of a subject fluid in a
dispersing fluid, with these fluids optionally separated by one or
more intermediate fluids. These fluids can be selected among
essentially any fluids (liquids, gases, and the like) by those of
ordinary skill in the art, by considering the relationship between
the fluids. For example, the subject fluid and the dispersing fluid
are selected to be immiscible within the timescale of formation of
the dispersed portions. Where the dispersed portions remain liquid
for a significant period of time, the fluids should be
significantly immiscible. Where, after formation of dispersed
portions, the dispersed portions are quickly hardened by
polymerization or the like, the fluids need not be as immiscible.
Those of ordinary skill in the art can select suitable immiscible
fluids, using contact angle measurements or the like, to carry out
various techniques of the invention.
[0075] In some embodiments, a discontinuous section has a maximum
dimension, and the size ratio of the section having the largest
maximum dimension to that having the smallest maximum dimension is
at least 10:1, at least 25:1, at least 50:1, at least 100:1, etc.
The discontinuous sections may have a maximum cross-sectional
dimension of less than 50 microns, less than 25 microns, less than
10 microns, less than 5 microns, less than 1 micron, and so on.
[0076] Subject fluid dispersion can be controlled by those of
ordinary skill in the art, based on the teachings herein, as well
as available teachings in the field of flow-focusing. Reference can
be made, for example, to "Generation of Steady Liquid Microthreads
and Micron-Sized Monodispersed Sprays and Gas Streams," Phys. Rev.
Lett., 80:2, Jan. 12, 1998, Ganan-Calvo, as well as numerous other
texts, for selection of fluids to carry out the purposes of various
embodiments of the invention. As will be more fully appreciated
from the examples below, control of dispersing fluid flow rate, and
ratio between the flow rates of dispersing and subject fluids, can
be used to control subject fluid stream and/or dispersion size, and
monodispersity versus polydispersity in fluid dispersions. The
microfluidic devices of the present invention, coupled with flow
rate and ratio control as taught herein, allow significantly
improved control and range. The size of the dispersed portion can
range down to less than one micron in diameter. In some
embodiments, the ratio of the flow rate of the subject fluid to the
dispersing fluid is less than 1:5, less than 1:25, less than 1:50,
less than 1:100, less than 1:250, less than 1:400, etc. The flow
rate of the dispersing fluid within a microfluidic channel can be
any suitable rate. For example, the flow rate may be between
6.times.10.sup.-5 and 1.times.10.sup.-2 milliliters per second,
1.times.10.sup.-4 and 1.times.10.sup.-3 milliliters per second, and
the like.
[0077] Many dispersions have bulk properties (e.g. rheology; how
the dispersion(s) flows, and optionally other properties such as
optical properties, taste, feel, etc., influenced by the dispersion
size and the dispersion size distribution. Typical prior art
techniques, such as prior art flow focusing techniques, most
commonly involve monodisperse systems. The present invention also
involves control of conditions that bidisperse and polydisperse
discontinuous section distributions result, and this can be useful
when influencing the bulk properties by altering the discontinuous
size distribution, etc.
[0078] The invention, in some embodiments, can be used to form a
variety of dispersed fluid sections or particles for use in
medicine (e.g., pharmaceuticals), skin care products (e.g. lotions,
shower gels), foods (e.g. salad dressings, ice cream), ink
encapsulation, paint, micro-templating of micro-engineered
materials (e.g., photonic crystals, smart materials, etc.), foams,
and the like. Highly monodisperse and concentrated liquid crystal
droplets produced according to various embodiments of the invention
can self-organize into two and three dimensional structures, and
these can be used in, for example, novel optical devices.
[0079] In some embodiments, a gas-liquid dispersion may be formed
to create a foam. As the volume percent of a gas in a gas-liquid
dispersion increases, individual gas bubbles may lose their
spherical shape as they are forced against each other. If
constrained by one or more surfaces, these spheres may be
compressed to disks, but will typically maintain a circular shape
pattern when viewed through the compressing surface. Typically, a
dispersion is called a foam when the gas bubbles become
non-spherical, or polygonal, at higher volume percentages. Although
many factors, for example, dispersion size, viscosity, and surface
tension may affect when a foam is formed, in some embodiments,
foams form (non-spherical bubbles) when the volume percent of gas
in the gas-liquid dispersion exceeds, for example, 75, 80, 85, 90
or 95.
[0080] A variety of materials and methods can be used to form
components of the system, according to one set of embodiments of
the present invention. In some cases various materials selected
lend themselves to various methods. For example, components of
certain embodiments of the invention can be formed from solid
materials, in which the channels can be formed via micromachining,
film deposition processes such as spin coating and chemical vapor
deposition, laser fabrication, photolithographic techniques,
etching methods including wet chemical or plasma processes, and the
like. See, for example, Angell, et al., Scientific American
248:44-55 (1983). In one embodiment, at least a portion of the
system is formed of silicon by etching features in a silicon chip.
Technology for precise and efficient fabrication of devices of
various embodiments of the invention from silicon is known. In
another embodiment that section (or other sections) can be formed
of a polymer, and can be an elastomeric polymer, or
polytetrafluoroethylene (PTFE; Teflon.RTM.), or the like.
[0081] Different components can be fabricated of different
materials. For example, a base portion of a microfluidic device
including a bottom wall and side walls can be fabricated from an
opaque material such as silicon or PDMS, and a top portion, or
cover, can be fabricated from a transparent material such as glass
or a transparent polymer, for observation and control of the
fluidic process. Components can be coated so as to expose a desired
chemical functionality to fluids that contact interior channel
walls, where base supporting material does not have the precise,
desired functionality. For example, components can be fabricated as
illustrated, with interior channel walls coated with another
material.
[0082] Material used to fabricate various devices of the invention,
or material used to coat interior walls of fluid channels, may
desirably be selected from among those materials that will not
adversely affect or be affected by fluid flowing through the
device, e.g., material(s) that is chemically inert in the presence
of fluids at working temperatures and pressures that are to be used
within the device.
[0083] In one embodiment, certain components of the invention are
fabricated from polymeric and/or flexible and/or elastomeric
materials, and can be conveniently formed of a hardenable fluid,
facilitating fabrication via molding (e.g. replica molding,
injection molding, cast molding, etc.). The hardenable fluid can be
essentially any fluid art that can be induced to solidify, or that
spontaneously solidifies, into a solid capable of containing and
transporting fluids contemplated for use in and with the
microfluidic network structures. In one embodiment, the hardenable
fluid comprises a polymeric liquid or a liquid polymeric precursor
(i.e. a "prepolymer"). Suitable polymeric liquids can include, for
example, thermoplastic polymers, thermoset polymers, or mixture of
such polymers heated above their melting point; or a solution of
one or more polymers in a suitable solvent, which solution forms a
solid polymeric material upon removal of the solvent, for example,
by evaporation. Such polymeric materials, which can be solidified
from, for example, a melt state or by solvent evaporation, are well
known to those of ordinary skill in the art. A variety polymeric
materials, many of which are elastomeric, are suitable, and are
also suitable for forming molds or mold masters, for embodiments
where one or both of the mold masters is composed of an elastomeric
material. A non-limiting list of examples of such polymers includes
polymers of the general classes of silicone polymers, epoxy
polymers, and acrylate polymers. Epoxy polymers are characterized
by the presence of a three-membered cyclic ether group commonly
referred to as an epoxy group, 1,2-epoxide, or oxirane. For
example, diglycidyl ethers of bisphenol A can be used, in addition
to compounds based on aromatic amine, triazine, and cycloaliphatic
backbones. Another example includes the well-known Novolac
polymers. Examples of silicone elastomers suitable for use
according to certain embodiments of the invention include those
formed from precursors including the chlorosilanes such as
methylchlorosilanes, ethylchlorosilanes, and phenylchlorosilanes,
and the like.
[0084] Silicone polymers are preferred in one set of embodiments,
for example, the silicone elastomer polydimethylsiloxane (PDMS).
Exemplary polydimethylsiloxane polymers include those sold under
the trademark Sylgard by Dow Chemical Co., Midland, Mich., and
particularly Sylgard 182, Sylgard 184, and Sylgard 186. Silicone
polymers including PDMS have several beneficial properties
simplifying fabrication of the microfluidic structures of certain
embodiments of the invention. For instance, such materials are
inexpensive, readily available, and can be solidified from a
prepolymeric liquid via curing with heat. For example, PDMSs are
typically curable by exposure of the prepolymeric liquid to
temperatures of about, for example, 65.degree. C. to about
75.degree. C. for exposure times of about, for example, 1 hour.
Also, silicone polymers, such as PDMS, can be elastomeric and thus
may be useful for forming very small features with relatively high
aspect ratios, necessary in certain embodiments of the invention.
Flexible (e.g. elastomeric) molds or masters can be advantageous in
this regard.
[0085] One advantage of forming structures such as microfluidic
structures of various embodiments of the invention from silicone
polymers, such as PDMS, is the ability of such polymers to be
oxidized, for example by exposure to an oxygen-containing plasma
such as an air plasma, so that the oxidized structures contain at
their surface chemical groups capable of cross-linking to other
oxidized silicone polymer surfaces or to the oxidized surfaces of a
variety of other polymeric and non-polymeric materials. Thus,
components can be fabricated and then oxidized and essentially
irreversibly sealed to other silicone polymer surfaces, or to the
surfaces of other substrates reactive with the oxidized silicone
polymer surfaces, without the need for separate adhesives or other
sealing means. In most cases, sealing can be completed simply by
contacting an oxidized silicone surface to another surface without
the need to apply auxiliary pressure to form the seal. That is, the
pre-oxidized silicone surface acts as a contact adhesive against
suitable mating surfaces. Specifically, in addition to being
irreversibly sealable to itself, oxidized silicone such as oxidized
PDMS can also be sealed irreversibly to a range of oxidized
materials other than itself including, for example, glass, silicon,
silicon oxide, quartz, silicon nitride, polyethylene, polystyrene,
glassy carbon, and epoxy polymers, which have been oxidized in a
similar fashion to the PDMS surface (for example, via exposure to
an oxygen-containing plasma). Oxidation and sealing methods useful
in the context of the present invention, as well as overall molding
techniques, are described in Duffy et al., Rapid Prototyping of
Microfluidic Systems and Polydimethylsiloxane, Analytical
Chemistry, Vol. 70, pages 474-480, 1998, incorporated herein by
reference.
[0086] Another advantage to forming microfluidic structures of
various embodiments of the invention (or interior, fluid-contacting
surfaces) from oxidized silicone polymers is that these surfaces
can be much more hydrophilic than the surfaces of typical
elastomeric polymers (where a hydrophilic interior surface is
desired). Such hydrophilic channel surfaces can thus be more easily
filled and wetted with aqueous solutions than can structures
comprised of typical, unoxidized elastomeric polymers or other
hydrophobic materials. Thus, certain devices of the invention can
be made with surfaces that are more hydrophilic than unoxidized
elastomeric polymers.
[0087] In some embodiments, it may be desirable to make a channel
surface hydrophobic. One non-limiting method for making a channel
surface hydrophobic comprises contacting the channel surface with
an agent that confers hydrophobicity to the channel surface. For
example, in some embodiments, a channel surface may be contacted
(e.g., flushed) with Aquapel (a commercial auto glass treatment)
(PPG Industries, Pittsburgh, Pa.). In some embodiments, a channel
surface contacted with an agent that confers hydrophobicity may be
subsequently purged with air. In some embodiments, the channel may
be heated (e.g., baked) to evaporate solvent that contains the
agent that confers hydrophobicity.
[0088] Thus, in one aspect of the invention, a surface of a
microfluidic channel may be modified to facilitate the production
of emulsions such as multiple emulsions. In some cases, the surface
may be modified by coating a sol-gel onto at least a portion of a
microfluidic channel. As is known to those of ordinary skill in the
art, a sol-gel is a material that can be in a sol or a gel state,
and typically includes polymers. The gel state typically contains a
polymeric network containing a liquid phase, and can be produced
from the sol state by removing solvent from the sol, e.g., via
drying or heating techniques. In some cases, as discussed below,
the sol may be pretreated before being used, for instance, by
causing some polymerization to occur within the sol.
[0089] In some embodiments, the sol-gel coating may be chosen to
have certain properties, for example, having a certain
hydrophobicity. The properties of the coating may be controlled by
controlling the composition of the sol-gel (for example, by using
certain materials or polymers within the sol-gel), and/or by
modifying the coating, for instance, by exposing the coating to a
polymerization reaction to react a polymer to the sol-gel coating,
as discussed below.
[0090] For example, the sol-gel coating may be made more
hydrophobic by incorporating a hydrophobic polymer in the sol-gel.
For instance, the sol-gel may contain one or more silanes, for
example, a fluorosilane (i.e., a silane containing at least one
fluorine atom) such as heptadecafluorosilane, or other silanes such
as methyltriethoxy silane (MTES) or a silane containing one or more
lipid chains, such as octadecylsilane or other
CH.sub.3(CH.sub.2).sub.n-- silanes, where n can be any suitable
integer. For instance, n may be greater than 1, 5, or 10, and less
than about 20, 25, or 30. The silanes may also optionally include
other groups, such as alkoxide groups, for instance,
octadecyltrimethoxysilane. In general, most silanes can be used in
the sol-gel, with the particular silane being chosen on the basis
of desired properties such as hydrophobicity. Other silanes (e.g.,
having shorter or longer chain lengths) may also be chosen in other
embodiments of the invention, depending on factors such as the
relative hydrophobicity or hydrophilicity desired. In some cases,
the silanes may contain other groups, for example, groups such as
amines, which would make the sol-gel more hydrophilic. Non-limiting
examples include diamine silane, triamine silane, or
N-[3-(trimethoxysilyl)propyl] ethylene diamine silane. The silanes
may be reacted to form oligomers or polymers within the sol-gel,
and the degree of polymerization (e.g., the lengths of the
oligomers or polymers) may be controlled by controlling the
reaction conditions, for example by controlling the temperature,
amount of acid present, or the like. In some cases, more than one
silane may be present in the sol-gel. For instance, the sol-gel may
include fluorosilanes to cause the resulting sol-gel to exhibit
greater hydrophobicity, and other silanes (or other compounds) that
facilitate the production of polymers. In some cases, materials
able to produce SiO.sub.2 compounds to facilitate polymerization
may be present, for example, TEOS (tetraethyl orthosilicate).
[0091] It should be understood that the sol-gel is not limited to
containing only silanes, and other materials may be present in
addition to, or in place of, the silanes. For instance, the coating
may include one or more metal oxides, such as SiO.sub.2, vanadia
(V.sub.2O.sub.5), titania (TiO.sub.2), and/or alumina
(Al.sub.2O.sub.3).
[0092] In some instances, the microfluidic channel is constructed
from a material suitable to receive the sol-gel, for example,
glass, metal oxides, or polymers such as polydimethylsiloxane
(PDMS) and other siloxane polymers. For example, in some cases, the
microfluidic channel may be one in which contains silicon atoms,
and in certain instances, the microfluidic channel may be chosen
such that it contains silanol (Si--OH) groups, or can be modified
to have silanol groups. For instance, the microfluidic channel may
be exposed to an oxygen plasma, an oxidant, or a strong acid cause
the formation of silanol groups on the microfluidic channel.
[0093] The sol-gel may be present as a coating on the microfluidic
channel, and the coating may have any suitable thickness. For
instance, the coating may have a thickness of no more than about
100 micrometers, no more than about 30 micrometers, no more than
about 10 micrometers, no more than about 3 micrometers, or no more
than about 1 micrometer. Thicker coatings may be desirable in some
cases, for instance, in applications in which higher chemical
resistance is desired. However, thinner coatings may be desirable
in other applications, for instance, within relatively small
microfluidic channels.
[0094] In one set of embodiments, the hydrophobicity of the sol-gel
coating can be controlled, for instance, such that a first portion
of the sol-gel coating is relatively hydrophobic, and a second
portion of the sol-gel coating is relatively hydrophobic. The
hydrophobicity of the coating can be determined using techniques
known to those of ordinary skill in the art, for example, using
contact angle measurements such as those discussed below. For
instance, in some cases, a first portion of a microfluidic channel
may have a hydrophobicity that favors an organic solvent to water,
while a second portion may have a hydrophobicity that favors water
to the organic solvent.
[0095] The hydrophobicity of the sol-gel coating can be modified,
for instance, by exposing at least a portion of the sol-gel coating
to a polymerization reaction to react a polymer to the sol-gel
coating. The polymer reacted to the sol-gel coating may be any
suitable polymer, and may be chosen to have certain hydrophobicity
properties. For instance, the polymer may be chosen to be more
hydrophobic or more hydrophilic than the microfluidic channel
and/or the sol-gel coating. As an example, a hydrophilic polymer
that could be used is poly(acrylic acid).
[0096] The polymer may be added to the sol-gel coating by supplying
the polymer in monomeric (or oligomeric) form to the sol-gel
coating (e.g., in solution), and causing a polymerization reaction
to occur between the polymer and the sol-gel. For instance, free
radical polymerization may be used to cause bonding of the polymer
to the sol-gel coating. In some embodiments, a reaction such as
free radical polymerization may be initiated by exposing the
reactants to heat and/or light, such as ultraviolet (UV) light,
optionally in the presence of a photoinitiator able to produce free
radicals (e.g., via molecular cleavage) upon exposure to light.
Those of ordinary skill in the art will be aware of many such
photoinitiators, many of which are commercially available, such as
Irgacur 2959 (Ciba Specialty Chemicals) or
2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (SIH6200.0,
ABCR GmbH & Co. KG).
[0097] The photoinitiator may be included with the polymer added to
the sol-gel coating, or in some cases, the photoinitiator may be
present within the sol-gel coating. For instance, a photoinitiator
may be contained within the sol-gel coating, and activated upon
exposure to light. The photoinitiator may also be conjugated or
bonded to a component of the sol-gel coating, for example, to a
silane. As an example, a photoinitiator such as Irgacur 2959 may be
conjugated to a silane-isocyanate via a urethane bond, where a
primary alcohol on the photoinitiator may participate in
nucleophilic addition with the isocyanate group, which may produce
a urethane bond.
[0098] It should be noted that only a portion of the sol-gel
coating may be reacted with a polymer, in some embodiments of the
invention. For instance, the monomer and/or the photoinitiator may
be exposed to only a portion of the microfluidic channel, or the
polymerization reaction may be initiated in only a portion of the
microfluidic channel. As a particular example, a portion of the
microfluidic channel may be exposed to light, while other portions
are prevented from being exposed to light, for instance, by the use
of masks or filters. Accordingly, different portions of the
microfluidic channel may exhibit different hydrophobicities, as
polymerization does not occur everywhere on the microfluidic
channel. As another example, the microfluidic channel may be
exposed to UV light by projecting a de-magnified image of an
exposure pattern onto the microfluidic channel. In some cases,
small resolutions (e.g., 1 micrometer, or less) may be achieved by
projection techniques.
[0099] Another aspect of the present invention is generally
directed at systems and methods for coating such a sol-gel onto at
least a portion of a microfluidic channel. In one set of
embodiments, a microfluidic channel is exposed to a sol, which is
then treated to form a sol-gel coating. In some cases, the sol can
also be pretreated to cause partial polymerization to occur. Extra
sol-gel coating may optionally be removed from the microfluidic
channel. In some cases, as discussed, a portion of the coating may
be treated to alter its hydrophobicity (or other properties), for
instance, by exposing the coating to a solution containing a
monomer and/or an oligomer, and causing polymerization of the
monomer and/or oligomer to occur with the coating.
[0100] The sol may be contained within a solvent, which can also
contain other compounds such as photoinitiators including those
described above. In some cases, the sol may also comprise one or
more silane compounds. The sol may be treated to form a gel using
any suitable technique, for example, by removing the solvent using
chemical or physical techniques, such as heat. For instance, the
sol may be exposed to a temperature of at least about 150.degree.
C., at least about 200.degree. C., or at least about 250.degree.
C., which may be used to drive off or vaporize at least some of the
solvent. As a specific example, the sol may be exposed to a
hotplate set to reach a temperature of at least about 200.degree.
C. or at least about 250.degree. C., and exposure of the sol to the
hotplate may cause at least some of the solvent to be driven off or
vaporized. In some cases, however, the sol-gel reaction may proceed
even in the absence of heat, e.g., at room temperature. Thus, for
instance, the sol may be left alone for a while (e.g., about an
hour, about a day, etc.), and/or air or other gases may be passed
over the sol, to allow the sol-gel reaction to proceed.
[0101] In some cases, any ungelled sol that is still present may be
removed from the microfluidic channel. The ungelled sol may be
actively removed, e.g., physically, by the application of pressure
or the addition of a compound to the microfluidic channel, etc., or
the ungelled sol may be removed passively in some cases. For
instance, in some embodiments, a sol present within a microfluidic
channel may be heated to vaporize solvent, which builds up in a
gaseous state within the microfluidic channels, thereby increasing
pressure within the microfluidic channels. The pressure, in some
cases, may be enough to cause at least some of the ungelled sol to
be removed or "blown" out of the microfluidic channels.
[0102] In certain embodiments, the sol is pretreated to cause
partial polymerization to occur, prior to exposure to the
microfluidic channel. For instance, the sol may be treated such
that partial polymerization occurs within the sol. The sol may be
treated, for example, by exposing the sol to an acid or
temperatures that are sufficient to cause at least some gellation
to occur. In some cases, the temperature may be less than the
temperature the sol will be exposed to when added to the
microfluidic channel. Some polymerization of the sol may occur, but
the polymerization may be stopped before reaching completion, for
instance, by reducing the temperature. Thus, within the sol, some
oligomers may form (which may not necessarily be well-characterized
in terms of length), although full polymerization has not yet
occurred. The partially treated sol may then be added to the
microfluidic channel, as discussed above.
[0103] In certain embodiments, a portion of the coating may be
treated to alter its hydrophobicity (or other properties) after the
coating has been introduced to the microfluidic channel. In some
cases, the coating is exposed to a solution containing a monomer
and/or an oligomer, which is then polymerized to bond to the
coating, as discussed above. For instance, a portion of the coating
may be exposed to heat or to light such as ultraviolet right, which
may be used to initiate a free radical polymerization reaction to
cause polymerization to occur. Optionally, a photoinitiator may be
present, e.g., within the sol-gel coating, to facilitate this
reaction.
[0104] Additional details of such coatings and other systems may be
seen in U.S. Provisional Patent Application Ser. No. 61/040,442,
filed Mar. 28, 2008, entitled "Surfaces, Including Microfluidic
Channels, With Controlled Wetting Properties," by Abate, et al.;
and an International Patent Application filed Feb. 11, 2009,
entitled "Surfaces, Including Microfluidic Channels, With
Controlled Wetting Properties," by Abate, et al., each incorporated
herein by reference in their entireties.
[0105] In one embodiment, a bottom wall is formed of a material
different from one or more side walls or a top wall, or other
components. For example, the interior surface of a bottom wall can
comprise the surface of a silicon wafer or microchip, or other
substrate. Other components can, as described above, be sealed to
such alternative substrates. Where it is desired to seal a
component comprising a silicone polymer (e.g. PDMS) to a substrate
(bottom wall) of different material, it is preferred that the
substrate be selected from the group of materials to which oxidized
silicone polymer is able to irreversibly seal (e.g., glass,
silicon, silicon oxide, quartz, silicon nitride, polyethylene,
polystyrene, epoxy polymers, and glassy carbon surfaces which have
been oxidized). Alternatively, other sealing techniques can be
used, as would be apparent to those of ordinary skill in the art,
including, but not limited to, the use of separate adhesives,
thermal bonding, solvent bonding, ultrasonic welding, etc.
[0106] In another embodiment, the present invention generally
relates to systems and methods for creating emulsions, including
multiple emulsions. In some cases, emulsions, including multiple
emulsions, may be created through a "triggering" process, where a
fluidic droplet or other entity is used to create one or more
nestings of droplets containing the fluidic droplet or other
entity. In such a manner, multiple emulsions may be formed in some
cases, e.g., triple emulsions, quadruple emulsions, quintuple
emulsions, etc. In certain embodiments, a first droplet (or other
entity) is used to "plug" a channel; fluid pooling behind the
droplet pushes the droplet through the channel to form the
emulsion. This process may be repeated to create multiple emulsions
in some cases. Other aspects of the present invention generally
relate to systems for producing such emulsions, methods of using
such emulsions, methods of promoting such emulsions, or the
like.
[0107] Thus, in certain embodiments, the present invention
generally relates to emulsions, including multiple emulsions, and
to methods and apparatuses for making such emulsions. A "multiple
emulsion," as used herein, describes larger droplets that contain
one or more smaller droplets therein. The larger droplets may be
suspended in a third fluid. In certain embodiments, larger degrees
of nesting within the multiple emulsion are possible. For example,
an emulsion may contain droplets containing smaller droplets
therein, where at least some of the smaller droplets contain even
smaller droplets therein, etc. Multiple emulsions can be useful for
encapsulating species such as pharmaceutical agents, cells,
chemicals, or the like. As described below, multiple emulsions can
be formed in certain embodiments with generally precise
repeatability.
[0108] Fields in which emulsions or multiple emulsions may prove
useful include, for example, food, beverage, health and beauty
aids, paints and coatings, and drugs and drug delivery. For
instance, a precise quantity of a drug, pharmaceutical, or other
agent can be contained within an emulsion, or in some instances,
cells can be contained within a droplet, and the cells can be
stored and/or delivered. Other species that can be stored and/or
delivered include, for example, biochemical species such as nucleic
acids such as siRNA, RNAi and DNA, proteins, peptides, or enzymes,
or the like. Additional species that can be incorporated within an
emulsion include, but are not limited to, nanoparticles, quantum
dots, fragrances, proteins, indicators, dyes, fluorescent species,
chemicals, or the like. An emulsion can also serve as a reaction
vessel in certain cases, such as for controlling chemical
reactions, or for in vitro transcription and translation, e.g., for
directed evolution technology.
[0109] Using the methods and devices described herein, in some
embodiments, an emulsion having a consistent size and/or number of
droplets can be produced, and/or a consistent ratio of size and/or
number of outer droplets to inner droplets (or other such ratios)
can be produced for cases involving multiple emulsions. For
example, in some cases, a single droplet within an outer droplet of
predictable size can be used to provide a specific quantity of a
drug. In addition, combinations of compounds or drugs may be
stored, transported, or delivered in a droplet. For instance,
hydrophobic and hydrophilic species can be delivered in a single,
multiple emulsion droplet, as the droplet can include both
hydrophilic and hydrophobic portions. The amount and concentration
of each of these portions can be consistently controlled according
to certain embodiments of the invention, which can provide for a
predictable and consistent ratio of two or more species in a
multiple emulsion droplet.
[0110] In one aspect, an emulsion may be created through a
"triggering" process, where a droplet or other entity is used to
create one or more nestings of fluidic droplets containing the
droplet or other entity. Other entities besides fluidic droplets,
for instance, cells or gel particles, may also be used in certain
embodiments.
[0111] More generally, various aspects of the invention are
directed to systems and methods for creating emulsions, including
multiple emulsions, using a process in which a deformable entity,
such as a fluidic droplet or a gel, at least partially plugs an
outlet channel, where the creation of a droplet containing the
deformable entity is "triggered" by pushing the deformable entity
into the outlet channel. The outlet channel may be, for instance, a
microfluidic channel, as is discussed below. Typically, droplet
formation cannot occur without this partial plugging (although
there may be a relatively low "error" rate in some embodiments),
and so the formation of the droplet is said to be "triggered" by
creating and releasing the partial plug of the deformable entity
into the outlet channel.
[0112] As used herein, a "deformable entity" is any entity able to
at least partially plug an outlet channel, where a carrying fluid
containing the deformable entity cannot flow past the deformable
entity into the outlet channel while the deformable entity at least
partially plugs the outlet channel. In some cases, the "plugging"
may be complete, i.e., viewing the outlet channel in cross-section,
it is not possible for a molecule of the carrying fluid to flow
through the outlet channel without crossing the deformable entity.
However, in other cases, the plugging may be partial, such that it
is theoretically possible for a molecule to enter into the outlet
channel without crossing the deformable entity, although the
carrying fluid may still be prevented from entering into the outlet
channel due to effects such as viscosity, hydrophobic repulsion,
charge repulsion, or the like.
[0113] Other examples may be seen in U.S. Provisional Application
No. 61/160,020, filed on Mar. 13, 2009, entitled "Controlled
Creation of Emulsions, Including Multiple Emulsions," by Weitz, et
al., incorporated herein by reference.
[0114] The following documents are incorporated herein by
reference: U.S. patent application Ser. No. 08/131,841, filed Oct.
4, 1993, entitled "Formation of Microstamped Patterns on Surfaces
and Derivative Articles," by Kumar, et al., now U.S. Pat. No.
5,512,131, issued Apr. 30, 1996; priority to International Patent
Application No. PCT/US96/03073, filed Mar. 1, 1996, entitled
"Microcontact Printing on Surfaces and Derivative Articles," by
Whitesides, et al., published as WO 96/29629 on Jun. 26, 1996; U.S.
patent application Ser. No. 09/004,583, filed Jan. 8, 1998,
entitled "Method of Forming Articles Including Waveguides via
Capillary Micromolding and Microtransfer Molding," by Kim, et al.,
now U.S. Pat. No. 6,355,198, issued Mar. 12, 2002; International
Patent Application No. PCT/US01/16973, filed May 25, 2001, entitled
"Microfluidic Systems including Three-Dimensionally Arrayed Channel
Networks," by Anderson, et al., published as WO 01/89787 on Nov.
29, 2001; S. Provisional Patent Application Ser. No. 60/392,195,
filed Jun. 28, 2002, entitled "Multiphase Microfluidic System and
Method," by Stone, et al.; U.S. Provisional Patent Application Ser.
No. 60/424,042, filed Nov. 5, 2002, entitled "Method and Apparatus
for Fluid Dispersion," by Link, et al.; U.S. Provisional Patent
Application Ser. No. 60/461,954, filed Apr. 10, 2003, entitled
"Formation and Control of Fluidic Species," by Link, et al.;
International Patent Application No. PCT/US03/20542, filed Jun. 30,
2003, entitled "Method and Apparatus for Fluid Dispersion," by
Stone, et al., published as WO 2004/002627 on Jan. 8, 2004; U.S.
Provisional Patent Application Ser. No. 60/498,091, filed Aug. 27,
2003, entitled "Electronic Control of Fluidic Species," by Link, et
al.; international Patent Application No. PCT/US2004/010903, filed
Apr. 9, 2004, entitled "Formation and Control of Fluidic Species,"
by Link, et al., published as WO 2004/091763 on Oct. 28, 2004;
International Patent Application No. PCT/US2004/027912, filed Aug.
27, 2004, entitled "Electronic Control of Fluidic Species," by
Link, et al., published as WO 2005/021151 on Mar. 10, 2005; U.S.
patent application Ser. No. 11/024,228, filed Dec. 28, 2004,
entitled "Method and Apparatus for Fluid Dispersion," by Stone, et
al., published as U.S. Patent Application Publication No.
2005-0172476 on Aug. 11, 2005; U.S. Provisional Patent Application
Ser. No. 60/659,045, filed Mar. 4, 2005, entitled "Method and
Apparatus for Forming Multiple Emulsions," by Weitz, et al.; U.S.
Provisional Patent Application Ser. No. 60/659,046, filed Mar. 4,
2005, entitled "Systems and Methods of Forming Particles," by
Garstecki, et al.; and U.S. patent application Ser. No. 11/246,911,
filed Oct. 7, 2005, entitled "Formation and Control of Fluidic
Species," by Link, et al.
[0115] The function and advantage of these and other embodiments of
the present invention will be more fully understood from the
examples below. The following examples are intended to illustrate
the benefits of the present invention, but do not exemplify the
full scope of the invention.
Example 1
[0116] This example demonstrates the fabrication of a parallel drop
formation system.
[0117] An array of microfluidic drop formation devices was
fabricated from PDMS (polydimethylsiloxane) using standard
multilayer soft lithography. The fluidic channels were arranged in
a PDMS layer to have solid walls and ceilings but open floors.
Fabrication of the channels was completed by bonding the
channel-containing layer to a base of glass or PDMS. A channel in
one layer can be connected to a channel in an adjacent layer by
punching a hole in the ceiling of the lower layer channel.
[0118] In this example, the bottom-most layer contains an array of
microfluidic devices, which are not connected together within this
layer. This device layer was plasma bonded to a glass slide coated
with a thin layer of cured PDMS elastomer.
[0119] On top of the device layer was bonded a first distribution
channel layer containing an array of fluidic channels, with spacing
that matches that of the inlets in the device layer and with
sufficient length to cover the full row of devices. This single
first channel layer constituted the fluid distribution article for
a 1-D array of devices.
[0120] For a 2-D array of devices, a second channel layer was
bonded above the first, with a set of channels running
perpendicularly to the lower set and with appropriate length and
spacing to cover the inlets and outlets of the lower channels as
shown in FIG. 7.
[0121] To make a 3-D array of devices, several 2-D arrays and fluid
distribution articles were stacked in the following sequence
(building upwards from a glass slide): glass slide for bottom-most
rigid support; solid spacer layer; device layer; fluid distribution
article comprising a first channel layer and a second perpendicular
channel layer; second sequence of solid spacer layer; device layer;
fluid distribution article; and so on, for an arbitrary number of
iterations. The fluid distribution articles are served by a set of
distribution channels perpendicular to the device layers.
[0122] The assembled device array was operated by supplying fluids
through polyethylene surgical tubing using a syringe pump.
Example 2
[0123] This example demonstrates the calculation of channel
dimensions for a parallel microfluidic device.
[0124] As a sample calculation, the desirable channel dimensions to
serve a 5.times.5 array of T-junctions producing simple emulsion
droplets was estimated using the following equation, which is known
in the art:
R=[(12*.mu.*L)/(w*h.sup.3)]*{[1-[(192/.pi..sup.5)*(h/w)]].sup.-1},
where "R" is the resistance in a rectangular microchannel, ".mu."
is the fluid viscosity, "L" is the channel length, "w" is the
channel width, and "h" is the channel height. T-junctions with
channel length 4000 .mu.m, width 50 .mu.m, and height 25 .mu.m,
have resistance of about 100 kPa*s/.mu.L assuming a viscosity of
.mu.=1 mPa*s. If the first-generation distribution channels have
height 150 .mu.m, width 1500 .mu.m, and the distance between
adjacent devices is 10,000 .mu.m, then the resistance per segment
is R.sub.c1=0.2 kPa*s/.mu.L. This affords equal flow division
between the 5 devices at the 1% accuracy level. For the
second-generation distribution channels, increasing the height to
250 .mu.m and keeping the other dimensions the same gives
R.sub.c2=0.04 kPa*s/.mu.L, which again affords equal flow division
at the 1% level.
Example 3
[0125] This example demonstrates parallelization of double emulsion
formation.
[0126] Each dropmaking unit included two sequential cross junctions
as shown in FIG. 12. An array of units was molded in one monolithic
block of PDMS using standard soft lithography. Inlet and outlet
holes were hand-punched, and plasma bonding was used to seal the
microchannels to a glass base plate. Plasma bonding was again used
to seal a layer of distribution channels onto the array. To make
the channel surfaces in the devices hydrophobic for drop formation,
the assembled device was flushed with Aquapel (a commercial auto
glass treatment) and purged with air. The device was baked for
several hours to dry the remaining Aquapel.
[0127] To produce double emulsions, the following fluids were
injected through the distribution channels: 1-octanol as the
innermost phase, water with 0.5% (by weight) sodium dodecyl sulfate
("SDS", a surfactant) as the shell phase, and HFE-7500 oil with
1.8% (by weight) "R22" surfactant as the continuous phase (R22 is
the ammonium salt of Krytox 157 FSL oil, a commercially available
perfluorinated polyether). The total flow rates used were 250
microliters per hour for the innermost phase, 1000 microliters per
hour for the shell phase, and 4000 microliters per hour for the
continuous phase. Double emulsions of different sizes could be
formed by changing the flow rates and/or by using devices with
different sized microchannels. The distribution channels can be
adjusted for these cases, for example by using a calculation as in
Example 2. Those of ordinary skill in the art will recognize that
auxiliary components, not shown or described in detail herein, are
useful in implementing the invention. For example, sources of
various fluids, means for controlling pressures and/or flow rates
of these fluids as delivered to channels shown herein, etc. Those
of ordinary skill in the art will readily envision a variety of
other means and structures for performing the functions and/or
obtaining the results or advantages described herein, and each of
such variations or modifications is deemed to be within the scope
of the present invention. More generally, those skilled in the art
would readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that actual parameters, dimensions, materials, and
configurations will depend upon specific applications for which the
teachings of the present invention are used. Those skilled in the
art will recognize, or be able to ascertain using no more than
routine experimentation, many equivalents to the specific
embodiments of the invention described herein. It is, therefore, to
be understood that the foregoing embodiments are presented by way
of example only and that, within the scope of the appended claims
and equivalents thereto, the invention may be practiced otherwise
than as specifically described. The present invention is directed
to each individual feature, system, material and/or method
described herein. In addition, any combination of two or more such
features, systems, materials and/or methods, if such features,
systems, materials and/or methods are not mutually inconsistent, is
included within the scope of the present invention.
[0128] In the claims (as well as in the specification above), all
transitional phrases such as "comprising", "including", "carrying",
"having", "containing", "involving", "composed of", "made of",
"formed of" and the like are to be understood to be open-ended,
i.e. to mean including but not limited to. Only the transitional
phrases "consisting of" and "consisting essentially of" shall be
closed or semi-closed transitional phrases, respectively, as set
forth in the United States Patent Office Manual of Patent Examining
Procedures, section 2111.03.
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